SVD分析揭示的澳大利亚高压年际变化对中国夏季降水的可能影响

Possible impacts of the interannual variability of the Australian high on summertime rainfall in China as revealed by the SVD analysis.

中文关键词:  澳大利亚高压， 年际变化， 中国夏季降水

英文关键词:Australian high, Interannual variability, Summer rainfall

中文摘要:

      澳大利亚高压是东亚夏季风系统的重要成员之一，其对中国夏季气候存在显著影响。为了进一步弄清年际时间尺度上的澳大利亚高压变化对中国东部夏季降水的影响，利用澳大利亚海平面气压和中国夏季降水站点资料，使用SVD和线性回归方法揭示了澳大利亚高压的年际变化与中国夏季降水异常的联系，得到：SVD的第1模态的时间系数与通常使用的澳大利亚高压指数相关可达到0.98。在有无考虑ENSO的影响时，SVD的第1模态均反映出澳大利亚高压的年际变化与中国江南地区夏季降水存在密切联系，也即澳大利亚高压增强（减弱）时，江南地区降水增多（减少）。澳大利亚高压对中国夏季降水的可能影响途径为：澳大利亚高压通过影响赤道纬向气流和越赤道气流并通过类似PJ波列的方式影响到中国东部地区：澳大利亚高压增强时，造成西太平洋副热带高压偏南、偏西，同时，105°E处越赤道气流显著加强，为江南地区提供充足水汽源，利于中国江南地区降水；澳大利亚高压减弱时，情况相反；在强（弱）澳大利亚高压年，印度尼西亚及热带辐合带海区SSTA负（正）异常使得低层风场的异常辐散（辐合），激发了澳大利亚南部以及西太平洋地区异常反气旋（气旋）环流，同时江南地区出现异常辐合（辐散），引起大气异常上升（下沉）运动，有利于中国江南地区夏季降水异常偏多（偏少）。

英文摘要:

      The Australian high as an important circulation member of the East Asian summer monsoon system has significant impacts on the summertime climate of China. By using the sea level pressure data from the NCEP/NCAR reanalysis data and the monthly mean data of rainfall at 107 stations in China， the relationships between the interannual variability of the Australian high and summer precipitation in China have been studied with the singular value decomposition (SVD) and regression methods. The time series of the coefficient for the first mode of the singular vector (SVD1) is found to be very highly correlated with the Australian high index (correlation:0.98), in agreement with the results in many other studies, showing that the SVD1 is able to well depict the variations of the Australian high. The first mode displays the close relationship between the interannual variability of Australian high and summer precipitation in the regions south of the Yangtze River. When the Australian high is stronger (weaker) than normal， summer precipitation in regions south of the Yangtze River will be significantly more (less) than normal. The Australia high influences summer precipitation in China via changing both the zonal and the cross equatorial flows in the equatorial region and via a way like the wave train P-J. When the Australian high is stronger than normal, the location of the west Pacific subtropical high seems to be more southern and western than normal， inducing the intensification of the cross equatorial flow at 105°E, which transports ample water vapor northeastward to the regions south of the Yangtze River and thus enhances rainfall there. When the Australian high is weaker than normal, the scenario is opposite. Negative SSTA in the regions around Indonesia and intertropical convergence zone during strong (weak) Australia high pressure years will cause anomalous divergence (convergence) in the lower troposphere, including the anomalous anti cyclonic (cyclonic) circulation in both the southern Australia and the northwest Pacific. Simultaneously, the anomalous convergence (divergence) is also induced in the regions south of the Yangtze River, resulting in the anomalous ascent (decent) of air, which eventually facilitates more (less) rainfall in the regions south of China in boreal summer.